180 Reflections on Heat. 



and, indeed, I found that a speaking-tube (a conical 

 brass tube, well polished on the inside) placed between 

 one of the bulbs of the thermoscope and a hollow ball 

 of thin copper 3 inches in diameter, which, being filled 

 with pounded ice, was presented to it at a distance of 

 12 inches, increased more than three times the effect of 

 the cold body. 



To use a rather strong metaphor, but one which ex- 

 presses perfectly the idea which I have conceived of the 

 mechanical operation in question, I will say that the 

 cold ball spoke at the larger opening of the speaking- 

 tube while the bulb of the thermoscope listened at the 

 smaller opening. 



If it is true that the particles which make up all 

 material bodies are agitated continually by very rapid 

 vibratory motions, and that, in consequence of these 

 motions, all bodies at all temperatures send continually 

 from every point of their surfaces rays or undulations 

 similar to the undulations caused in the air by the 

 vibration of sonorous bodies; and if bodies of different 

 temperatures act one upon another at a distance, by 

 means of these rays or undulations, working simultane- 

 ously an interchange in temperature and gradually 

 bringing about a mean intermediate temperature, we 

 ought then to regard the cooling of a warm body as the 

 result of the actual and positive operation of the sur- 

 rounding bodies less warm than itself; and since the 

 rays coming from warm bodies, and, as a consequence, 

 from cold bodies, are reflected in great measure by the 

 polished surfaces of opaque bodies, and since the rays 

 which are reflected produce little or no effect on the 

 bodies at whose surfaces they are reflected, we might 

 conclude a priori that opaque polished bodies ought to 



